Re: [electricboats] LifePo4 build questions

The weight of those SAB 60280 cells isn't shown at Battery Hookup, but when I look elsewhere I see numbers over 3kg per cell.  That's quite heavy, as I see (for example) Gotion 52Ah cells that come in slightly under 1kg.  $240 for 1.4kWh is a good price for sure, but I suspect that's at least in part due to their poor energy density.

In my experience you can't charge multiple modules with their own BMS in series with just one charger . . . one of the modules will hit 100% SOC before the others and no longer pass charge current to the others.  I've heard of some BMSs that can bypass charge current around their cells, so with such a BMS it seems doable.

I'm usually after maximum energy density, so I go the route of assembling separate cells rather than putting a few 12.8V-nominal pre-made batteries in series.  It's also less expensive that way (if you order direct from China), but then packaging is on you.  Here is the current 10kWh battery I use on my boat:

https://www.youtube.com/watch?v=fmk1_ynLdwI

48V Battery Assembly for Electric Boat - YouTube Sixteen 200Ah LFP cells arranged as four modules of four cells each. Series arrangement yields 51.2V nominal times 200Ah, for 10.24 kWh capacity.There is a ... www.youtube.com

-Bobkart

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From: electricboats@groups.io <electricboats@groups.io> on behalf of shredderf16 <Shredderf16@sbcglobal.net>
Sent: Saturday, May 7, 2022 3:19 PM
To: electricboats@groups.io <electricboats@groups.io>
Subject: Re: [electricboats] LifePo4 build questions

 

Look at big battery.com or electric car parts.com. in addition check out Will Prowse Diy Solar channel on you tube, he does a lot of reviews. I would go with a 36v server rack, much easier than building your own.
Jerry Barth

On May 7, 2022, at 2:32 PM, Skray775 <kelly@skraye.com> wrote:

Thank you all for the help in my first thread about LifePo4 batteries. I have done a lot of research and have a question about building a bank of cells. 

System requirements, 36-volts, 50 to 100 aH, used to power a 36-volt trolling motor rated at 50 amp max.
Measured amp draw from trolling motor in a trash can full of water at half power setting was 10 amps. Full power setting could not be tested due to the limitation of my amp meter (25 amps). The power draw at setting 9 (out of 10) was 24 amps.

1) If you were building a battery would you build three 12-volt packs with three separate bms's, or construct one 36-volt pack with a single 36-volt bms?
2) Can you charge three 12-volt packs, each pack with its own BMS, wired in series, with a single 36-volt charger?
3) Your thoughts on SAB 60280 round cells vs prismatic cells. Used cells. 

Thank you for the help.